Topic: boggy

[the_genrl]

hi heres a carb bogging question but first, a little history. **Please read!  I know it's long but I need help big time!**

1977 750K was running but only at half-3/4 choke.  I cleaned carbs very well, put back together and found the bike would only idle and run at 5000rpm and above.  So i took the carbs apart again and found that the main jet needles were set on the leanest possible clip (very highest position.)  SO...i moved the clip to the center position, I guess as a starting point. 

Ok, now where we are today.  After reassembely for the 2nd time, the bike runs fine at all rpms, HOWEVER, when you mash it (twist grip real quick) the bike boggs and will keep bogging until A: you let back on the throttle or B: hold firm and the motor dies.  You can get to the higher rpms, but you have to turn the throttle slower (slow enough to be ANNOYING and not what i want  )

The accellerator pumps are working fine as you can see them squirt equaly and consistantly.  NOTE: I am not running an air filter only because it hasn't come in yet and i plan to put a stock one on.

NOW my main question is:  should i adjust the main jet needle setting again or wait for the air cleaner to come in?  Would simply running without an air cleaner cause this bog problem when under hard accelleration, or does the air cleaner really not matter that much and i should adjust the clip or get new jets? 

Again, acceleratior pumps are completely clean and working fine.  Everything for the carbs was throughly cleaned and everything is in good shape. Please, any advice would be extremely helpful!

[TwoTired]

The filter is important and adds restriction.  The effects are similar to partial choke application.  It will most likely require a change to some, if not all, of your carb metering adjustments.

[Quail "Owner of the comfortable k8"]

I have been waiting for a fellow "Redheaded Stepchild 1977-1978 CB750k" to talk about our carbs.  My bike is a dream at any thing over 1/3 throttle.  But aside from the adjustment you make under the top caps of 1-3-4 cyl, I can not find any other adjustments.  I had to get rid of the BOGGING by advancing the timing. 

MY QUESTION does anyone have any instructions on adjusting these carbs?

[TwoTired]

I have been waiting for a fellow "Redheaded Stepchild 1977-1978 CB750k" to talk about our carbs.  My bike is a dream at any thing over 1/3 throttle.  But aside from the adjustment you make under the top caps of 1-3-4 cyl, I can not find any other adjustments.  I had to get rid of the BOGGING by advancing the timing. 

MY QUESTION does anyone have any instructions on adjusting these carbs?

These carbs date from when anti-tampering was becoming prevalent.  I understand that there aren't any extra grooves in the needles, the pilot jets are pressed in, and the idle mixture screws have a limited range of adjustment.  (You have found these, haven't you?  They are vertical and are located just in front of the carb bowls.)  Still, the carbs operate on the same principles as the earlier carbs.

Have you determined whether operation below 1/3  throttle is too rich or too lean?   Are your spark plug insulators sooty or white when you operate the bike below 1/3 throttle for extended periods of time?

The attached chart shows what part of the carb is effective to adjust vs. throttle position.  It suggests that changing the clip position on the needle would be effective toward curing your below 1/3 throttle ills.  If only you had extra needle grooves, right?  Well then, perhaps needles from earlier carbs, that do have the extra grooves will give you the adjustment you need.  You'd probably have to compare the taper and length to what you have now and then adjust to direction you need.  Or, you can cut extra grooves in the needles you have now.  T'were it me, I'd explore different settings of the Idle Mixture Screws first.  But, these have a much narrower band of effect compared to the older carb's air screws.

[eldar]

I have this style of carb.  There are somethings I can say about it. The mails are replaceable, thus if you need to rejet these, you can. I have a feeling that these carbs start using the mains before the earlier carbs do since they are made to run leaner and have unadjustable lowspeed jets.

The lowspeed jets can supposedly be removed but there is no reason to if you have a decent carb tool for cleaning. HOWEVER, if you were to get the correct O.D. of the jet, you could possibly obtain brass stock tubing that is good quality to ensure correct O.D. and I.D. and MAKE your own low speed jets to make changes to low speed jetting. This may be a lot of work but could be worth looking into. IF you have tunning issues you cannot remedy them.

ALWAYS HAVE AN AIR FILTER INSTALLED WHEN MAKING ADJUSTMENTS!
If you do not, then you will endup starting all over anyways when you install the filter.

The first step is to make sure the float settings are correct at 14 - 15 MM. The manual says 14.5mm +- .5mm.

Also make sure the float seats are CLEAN and the floats are in good shape. This small little part will cause no end to headaches.

As for the idle screw. it DOES change to a wide degree your idle settings, I would have to say as much as the earlier carbs. I can adjust mine minutely with big changes.

If you have bogging problems then check idle screws and adjust them all 1 turn out as a start point.
REMEMBER, WITH THE 77-78 CARBS, OUT MEANS RICHER, IN MEANS LEANER!

[the_genrl]

hi everyone and thanks for the replys.

Quail:  yeah really.  It seems the 77 is a year honda wants us to forget about and not get parts for.  there are some other change over stuff too, for instance ive seen some 77s with the newer master cylinder...where mine has the older circle one? 

twotired:  i agree, i should put the airfilter on before i adjust things.  im just getting impacient!  I'm assuming that these carbs were messed with then, becuase all of the needles do infact have clip adjustments.  To further the theroy that they have been fooled with, when i first opened the carb tops the eclip was put on the leanest setting, why it ran only at idle and 5k up im guessing.  its strange becuase its quite a pain in the ass to change this on these carbs (with everything being internal and all), and the previous owner wasn't too "mechinicaly savoy".

eldar:   i have a found a place that sells different idle/main jets and am looking into it, but i think i will take your advice too and wait until i get my air filter on before i start screwing stuff up (pun intended).  The floats were all adjusted to something along that line (pain), float seats and needles are fine (rubber on these), and the idle screws are set without a filter (stupid me, that #2 one is terrible).   

thanks again everyone and im sure ill be back once i get and put the filter in!

[eldar]

#2 is the biggest problem in my book!   OK if you have slots on your needle, are your floats brass and round? If so then I dont think these are 77 carbs.

[the_genrl]

hi again and yes that #2 carb idle jet sucks!

Anyway, the floats are that "nitrile" or "nitrophile" or whatever that crap is and are two seperate floats.  oh and the thing that connects them is metal.  also, these carbs have a shaft that goes through all of them, through the carb body.  its all internal...kinda.  ummm, how else can i discribe...the caps bolt on with two little phillps screws and are rectangle with a circle bludge over top of where the slider is.

is that a help or should i take a picture?  boy i hope this isnt a bike with 1000 different parts from different years!

[eldar]

Well those floats are like a fiber? IS that what you meant? IF so then those should be correct floats. Now the float bowl I thought would be held on by 3 screws but no big deal. So it sounds as though some yahoo used different needles to correct a problem that is not that hard.

[the_genrl]

welp the air cleaner came in today.  I put the whole assembly back on the bike and in neutral, VROOM it seems the bog problem is gone.

how ever, i rode it for about a mile and notice the performance is garbage.  now i can hold and the bike wont die, but it sucks. 

i think i have to take the stupid carbs off and move the stupid needles back down a notch.    do you think im on the right track?

[eldar]

WHat makes this hard is that it sounds like the needles have been changed and maybe the main jets. Without knowing for sure, it is hard to say.  I know a 77K did not have slotted needles.
SO here is what I say now.

try riding and get the rpms to at least 5000 then kill the engine right there. Pull the plugs and see what they look like. This will give an indication of the main jets rich or lean condition.  We can go from there then without guessing so much.

Also, set your idle screw that is in front of the carbs bowls on the engine side, out 1.5 turns. This is standard for this year.
This screw controls FUEL for low speed, the earlier 750s the screw controlled AIR for low speed.  On our 77 - 78 bikes, turning the screw OUT makes it richer.

So check your plugs like I said before and see what they look like. Clean them and then idle for a few minutes and see what they look like again.

We can then make sure we are on the correct path.

Dont you just LOVE 4 carbs!

[Bob Wessner]

No! 

But then, in the hands of a good tuner (not me, unfortunately) you probably can't get better than a carb dedicated to each cylinder I would think.

[eldar]

Oh but Bob, you should be an expert by now!!!  I almost am on my carbs I think! Notice a previous post of mine where I talk about making my own low speed jets! See now that is an expert talking!

[jtb]

Genrl,
If your carbs are PD41A's (it will be at the bottom of the outside of #4 or #1 body), they were the carbs for the 77K.  They have slots for adjusting the needles.  The 78K came with PD42B carbs, no adjustment on the needles.  see http://www.hondachopper.com/carb.specs.html . 

I have a 77F2, with PD41B carbs.  I am running 115 mains, and have the needles in the bottom slot, and am happy.

John

[eldar]

They do have slots? 77 is the year emissions was required. Very odd. But when do manufactures do anything that is sensible.

[jtb]

Yeah, you're right Eldar, they never do anything when you expect.  I bought Keyster kits, and they didn't have slots in the needles, so I used the original ones instead.
It's my understanding that the carbs are the major difference between the 77' and 78's both K & F.

[eldar]

It is odd since I think the outsides look the same at least from pics I have seen they look the same.  For the most part though, tuning is handled the same way.

[jtb]

You're right, they do look alike, and on the F model, at least, the mains and slow jets are the same size.  All the specs are the same, the needles are not adjustable on the PD42A carbs (F3 or 78).  Go figure.  I'm glad that I can change the needles on mine.

John

[the_genrl]

ok so i rode some more and problem still there.  I KNOW this bike is supposed to be peppyer becuase when i first got it i was bogging but was still pretty get up and go. 

Ok to elder:  i checked my plugs (less than 4 miles on them) and i didnt really see anything too bad with them.  Tomorrow i will do what you say, run at 5k and kill, then take the plugs out.  I will also take a picture so you can tell me if they are rich or lean, im not sure.  i know the exhaust wasnt super black or anything that i could notice and smelled normal.

when i had the carbs out before, i remember reading the jets and they said "115" which is correct. the needles had something stamped on them too but i cant freaking remember what they said!  I'm sure they'll be in peices tomorrow so ill let you know 

To jtb:  Hey thanks alot for letting me know that i dont have a freak part.  Now i dont have to scramble ebay to get the right needles before the season is over.


Im getting the impression i shouldnt have touched the needles,  left them in the leanest position and waited for the air cleaner to come in..      my grandpop always used to say "If it aint broke..."  you know...

[Quail "Owner of the comfortable k8"]

the pilot jets are pressed in, and the idle mixture screws have a limited range of adjustment. (You have found these, haven't you? They are vertical and are located just in front of the carb bowls.) Still,

Well I must be blind ( i did not take off the air box to look) but I see no  idle mixture screws  to make adjustments on my carbs.  will not idle below 1000. jerky, stumbling, feeling up to 3100 rpm them as smooth as glass.  New spark plugs made no change.  1978 cb750k8

[TwoTired]

Well I must be blind ( i did not take off the air box to look) but I see no  idle mixture screws  to make adjustments on my carbs.  will not idle below 1000. jerky, stumbling, feeling up to 3100 rpm them as smooth as glass.  New spark plugs made no change.  1978 cb750k8

The idle mixture screws come straight down just in front of the carb bowls.  You need a double bevel geared, right angle screwdriver to adjust these.  Look at the bottoms of your carbs with mirror.

[eldar]

Quail, when you pull of the bowls, you see an indent about .5 inch. That  goes to the front of the carbs. The screw sits right in the indent.

I have a picture if you need it.

[the_genrl]

back again and i found a way to change the needle height without taking the carbs completely apart.  Boy did that save me some time!

SO they (the needles) are at the leanest position again, and now the bike runs great and the power is where it is supposed to be.

  HOWEVER    i think i have quail's problem now.  it has poor off idle response.  it seemed to go away when i was riding it but still that might have been because i was above 2k when i would mash it. 

HOW in gods name do i get rid of this annoying flat spot?!   when parked and idling, i give it gas and its boggy until about 2K, then its super responsive (just like yours quail.)   I probably have to adjust the idle jet screws, right eldar?   They are all set at 1.5 turns out like you said, but they need fine tuning i think which i dont know how to do.  I tryed listening by ear for a rise in rpm, but i dont really officaly how to do it and am olny guessing thats the right way.

[TwoTired]

From the Honda Shop Manual supplement fo the CB750 K7 ('77).
E. Adjustment.
Idle Speed:
1. Adjust the idle stop screw to allow the engine to run at an idle speed of 950 -1050 RPM.
2. Turn the pilot screw either in or out to obtain the highest idle speed.  Usually the correct setting will be 1 1/2 turns open from a fully closed position.
3. If the idle speed changes after adjusting the pilot screw, readjust the idle stop screw.


I read another post on this forum that said a tachometer capable of descriminating 50 RPM was most helpful during this procedure, particularly if your ears aren't practiced at noting minute RPM changes.

[eldar]

Well if there is a flat spot, it could be 2 things. The accel pump may not be getting actuated properly or the idle screws need adjustment.
Clean the plugs and let it idle for a while and check them. See if there is a carbon build up of if the plug is VERY clean.
On our bikes, out is RICHER while in is LEANER. The previous 750s air screw controlled air flow, our control fuel.  I remind this cause it took me a bit to remember that.

Just to mention it, your floats I think should be around 14 - 15 mm.

Unfortunetly I cannot give you exact settings sine now that a good base running has been achieved. It is fine tuning time now.

With the accel pump, supposedly you can see fuel being dumped in when hitting the gas. I never tried it so I dont know if the bike needs to be running for this to occur.